Heating system for a steam turbine energy producing plant

ABSTRACT

The system comprises a series of heaters arranged in cascade and fed with steam from drawoffs at pressures which progressively decrease from the steam boiler side to the condenser side of the plant. 
     In order to improve the efficiency of the plant with which the system is associated, the system comprises a plurality of biphase turbines arranged in cascade. The first of the turbines is fed from the drain of the heater at the highest pressure and the following turbines are each fed at least in part with the outlet liquid of the biphase turbine preceding it. These biphase turbines produce mechanical energy by recovery of the kinetic energy of the condensates of the heaters feeding them.

DESCRIPTION

1. Technical Field

The present invention relates to systems for heating condensed water employed in steam turbine energy producing plants such as electric power stations.

2. Background of the Prior Art

Heating systems for condensed water from steam turbines usually comprise a number of heaters disposed between the condenser and the steam boiler of the plant for heating the water condensed in the condenser. The heaters are fed with steam at different pressures from respective drawoffs on the turbine. Between certain heaters and the immediately adjacent heater fed with steam from a drawoff at a lower pressure, there is disposed a phase separator receiving the water-steam mixture from the blowoff of the heater associated with the drawoff at higher pressure and feeding the heater associated with the drawoff at a lower pressure, in parallel with this drawoff at lower pressure, with steam separated from said mixture in the phase separator device. Further, in nuclear pressurized water power stations, there is provided a superheater whose condensates are sent to the heater associated with the drawoff at the highest pressure through a phase separator.

With this arrangement, a part of the energy of the water-steam mixture of the blowoff of certain of the condensation exchangers, superheaters or heaters, are employed for contributing to the heating of the fluid of the condenser-turbine circuit in a condensation exchanger fed with the steam at a lower pressure. However, a part of this energy is lost in the form of heat in the main regulating valve provided in the blowoff pipe up-stream of the phase separator and in the phase separator.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to provide a heating system which enables a part of the energy lost in heating systems of the prior art to be used, so as to increase the overall energy efficiency of the energy producing plant with which the heating system is associated.

Another object of the invention is to provide a heating system for a steam turbine energy producing plant which, while it has an improved efficiency relative to the heating systems of the prior art, is simpler in construction than the latter.

A further object of the invention is to provide a heating system for a steam turbine energy producing plant, which reduces erosion encountered in conventional heating systems due to the high speed of the water-steam mixture at the outlet of the main regulating valve.

The invention such as defined in the claims enables these objects to be attained through the use of a biphase turbine which eliminates the need for the main regulating valve and phase separator of prior art system.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be apparent from the ensuing description of two particular embodiments thereof illustrated in the accompanying drawings in which:

FIG. 1 is a diagram of a conventional heating system for an electric power station employing fossil fuel;

FIG. 2 is a diagram of a heating system according to the invention for an electric power station employing fossil fuel;

FIG. 3 is a diagram of a conventional heating system for a nuclear electric power station, and

FIG. 4 is a diagram of a heating system according to the invention for a nuclear electric power station.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, there is shown the diagram of a conventional heating system having seven heaters R₁,R₂,R₃,R₄,R₅,R₆ and R₇. The heaters R₁ to R₇ heat the condensed water drawn off by an extracting pump PE from the condenser (not shown) of the steam turbine electric power station employing fossil fuel with which the heating system is associated.

The heater R₁ is fed with steam from a drawoff S₁ at 0.3 bar and at a rate of flow representing 4.5% of the total flow (100% by weight) delivered by the heater R₇ to the steam boiler (not shown) of the plant. The steam condensed in the heater R₁ is sent through a drain pipe P_(o) to the condenser. The second heater R₂ connected in series in the main condensed water circuit CP downstream of the heater R₁ is fed with steam from the drawoff S₂ at a pressure of 1 bar at a flow of 4.5% by weight. Third heater R₃ disposed downstream of the heater R₂ in the circuit CP, is fed with steam from a drawoff S₃ at a pressure of 2 bars at a flow representing 3% by weight of the total flow.

The flow of the main circuit CP at the outlet of the heater R₃ which represents 75% by weight of the total flow at the outlet of the heater R₇ is sent to a mixing heater or degassing tank R₄ which is fed with steam from a drawoff S₄ at a pressure of 4 bars and a flow representing 3.5% by weight of the total flow. Water from the heater R₃ and steam from the drawoff S₄ are mixed in the mixing heater R₄ and this mixture is drawn off by a feed pump PA which sends it to the heater R₅ which is fed with steam from a drawoff S₅ at a pressure of 9 bars and at a flow representing 7% by weight of the total flow. The water issuing from the heater R₅ is then sent to a heater R₆ which is fed with steam from a drawoff S₆ at a pressure of 18 bars and at a flow representing 7% by weight of the total flow.

The water issuing from the heater R₆ is again heated in the last heater R₇ which is fed with steam from a drawoff S₇ at a pressure of 36 bars and a flow representing 7.5% by weight of the total flow. The condensed water issuing from the heater R₇ therefore represents, as mentioned before, 100% of the total flow which is sent under a pressure of the order of 200 to 220 bars to the steam boiler GV (not shown) of the plant where this water is converted into steam so as to be sent back to the turbine (not shown).

The steam issuing from the drawoff S₇ is condensed in the heater R₇ and the condensates of this steam thus formed are discharged from the heater R₇ by way of a drain pipe P₁ connected to a first phase separator SP₁ through a main regulating valve SR₁. A motorized safety regulating valve V₁ is by-pass connected, relative to the main regulating valve SR₁, to the drain pipe P₁ so as to return if necessary the condensates of the drain pipe P₁ directly to the condenser. The regulating valves SR₁ and V₁ are controlled by a level regulator RN₁ which is adapted to regulate the level of water in the heater R₇. The mixture at 244° C. of the drain pipe P₁ is sent through the main regulating valve SR₁ into the phase separator SP₁ which separates the water from the steam resulting from the expansion, the steam being sent by way of a pipe CV₁ on the steam side to the heater R₆ and the water being sent by way of the pipe CE₁ on the water side to the heater R₆.

The condensates received in the heater R₆ are sent by way of a drain pipe P₂ to a phase separator SP₂ through a main regulating valve SR₂ with which there is connected in parallel a motorized safety regulating valve V₂. The condensates at 207° C. of the drain pipe P₂ are separated in the phase separator SP₂ and the steam is sent by way of a pipe CV₂ to the steam side of the heater R₅, whereas the water is sent by way of a pipe CE₂ to the water side of the heater R₅. The phase separator SP₂ and the regulating valves SR₂ and V₂ which are controlled by a level regulator RN₂ which regulates the water level in the heater R₆, operate in the same manner and perform the same function as the phase separator SP₁ and the regulating valves SR₁ and V₁ described hereinbefore.

The condensates at 175° C. received in the heater R₄ are sent by way of a drain pipe P₃ to the mixing heater R₄ through a main regulating valve SR₃ with which a motorized safety regulating valve V₃ is by-pass connected. The valves SR₃ and V₃ are controlled by a level regulator RN₃ which regulates the level of condensates in the heater R₅. The mixture flowing in the drain pipe P₃, which represents 21.5% by weight of the total flow, is mixed in the degasing tank R₄ with the water coming from the heater R₃ and the steam from the drawoff S₄ so that the feed pump PA has a flow representing 100% of the total flow.

The condensates received in the heater R₃ are sent by way of a drain pipe P₄ to a phase separator SP₃ through a main regulating valve SR₄ with which there is by-pass connected a motorized safety regulating valve V₄ which, as the valves V₁, V₂ and V₃ sends the condensates directly to the condenser in the event of an incident. The regulating valves SR₄ and V₄ are controlled by a level regulator RN₄ which regulates the water level in the heater R₃. The condensates at 120° C. of the drain pipe P₄ are divided in the phase separator SP₃ from which the steam is sent to the steam side of the heater R₂ by way of a pipe CV₃ whereas the water is sent to the water side of the heater R₂ by way of a pipe CE₃.

The drain pipe P₅ which receives the condensates at 100° C. issuing from the heater R₂ is connected at RA to a by-pass pipe CD which is connected between, on one hand, the condenser and, on the other hand, the main pipe CP, between the heaters R₂ and R₃. A motorized safety valve V₅ is disposed in the by-pass pipe CD between the connection RA and the condenser, and a main regulating valve SR₅ is disposed in the pipe CD between the connection RA and the connection of the pipe CD with the main pipe CP. The regulating valves SR₅ and V₅ are controlled by a level regulator RN₅ which regulates the water level in the heater R₂. A pump PR for receiving the condensates is disposed in the pipe CD between the connection RA and the regulating valve SR₅ so as to re-inject the condensates of the drain pipe P₅ into the main pipe CP. In the event the pump PR fails, the condensates are returned to the condenser by way of the safety regulating valve V₅.

In operation, a part of the heat energy of the mixture issuing from the heaters R₇, R₆, R₅, R₃ and R₂ is used for heating the water of the main circuit, either by direct re-injection into the latter from the heaters R₅ and R₂, or by sending it to the following heater after separation of the liquid phase and the steam phase in the phase separators SP₁, SP₂ and SP₃. However, a part of the energy of this mixture, present in the form of pressure, is lost in the phase separators which, moreover, have the drawback of being subject to a high degree of erosion owing to the high speed of the mixture at the outlet of the regulating valves.

These drawbacks are avoided in the heating system according to the invention, the diagram of which is shown in FIG. 2, in which the same reference numerals as those employed in FIG. 1 are used for designating similar elements. Further, note that the flows, pressures and temperatures at different points of the circuit according to the invention are substantially the same as those indicated in FIG. 1 and will not be mentioned again.

The heating system according to the invention of FIG. 2 differs essentially from that of FIG. 1 in that the main regulating valves SR₁, SR₂, SR₃ and SR₄ and the phase separators SP₁, SP₂ and SP₃ have been dispensed with and replaced by biphase turbines. Thus the biphase turbine TB₁ replaces the regulating valve SR₁ and the phase separator SP₁, the biphase turbine TB₂ replaces the regulating valve SR₂ and the phase separator SP₂, the biphase turbine TB₅ replaces the regulating valve SR₄ and the phase separator SP₃ and an additional biphase turbine TB₄ is disposed between the biphase turbines TB₃ and TB₅.

The biphase turbines are of special design which are fed with a mixture of a liquid and a gas or vapour for driving a shaft in rotation, thereby producing mechanical work while ensuring a separation of the liquid and the gas, so that the latter may be collected separately at the outlet of the turbine. As this type of turbine is known in particular from the U.S. Pat. Nos. 3,879,949; 3,972,195 and 4,087,261 to which reference may be made, no detailed description will be given in the present description.

The condensates of the heater R₇ are introduced in the biphase turbines TB₁ in accordance with the level in this heater by adjustment of the position of the regulator V'₁ of the biphase turbine TB₁ controlled by the level regulator RN₁. These condensates are sent to the condenser by way of the safety regulating valve V₁ in the event that the biphase turbine TB₁ is not operating. The steam separated in the latter is sent to the steam zone of the heater R₆ whereas the separated water returns to the condensates of the heater R₆. This mixture is introduced in the following biphase turbine TB₂ as a function of the level in the heater R₆ by adjustment of its regulator V'₂ which is controlled by the level regulator RN₂. In the event that the biphase turbine TB₂ is not operating, the mixture is sent to the condenser by way of the safety regulating valve V₂. The steam separated in the biphase turbine TB₂ is sent to the steam zone of the heater R₅ whereas the separated water returns to the condensates of this heater. Again, this mixture is introduced in the following biphase turbine TB₃ as a function of the level in the heater R₅ by adjustment of its regulator V'₃ which is controlled by the level regulator RN₃. In the event that the biphase turbine TB₃ does not operate, the mixture is sent to the condenser by way of the safety regulating valve V₃. The steam separated in the biphase turbine TB₃ is sent to the mixing heater R₄ whereas the separated water is sent directly to the following biphase turbine TB₄. The steam separated in the latter is sent to the steam zone of the heater R₃ whereas the separated water joins the condensates in this heater. Lastly, this mixture is introduced in the last biphase turbine TB₅ as a function of the level in the heater R₃ by adjustment of its regulator V'₄ which is controlled by the level regulator RN₄. In the event of stoppage of the biphase turbine TB₅, the mixture is sent to the condenser through the safety regulating valve V₄. The steam separated in the biphase turbine TB₅ is sent to the steam zone of the heater R₂ whereas the separated water joins the condensates of this heater at RA. The part downstream of this system operates thereafter as the corresponding part of the conventional heating system of FIG. 1.

In operation, the power of the mixture of water and steam in each of the biphase turbines is received on a common shaft A for driving an auxiliary alternator, a pump or some other means. By way of a modification the biphase turbines may not be coupled to the same shaft so that each biphase turbine drives its own auxiliary device.

Reference will now be made to FIG. 3 which shows a conventional heating system for a nuclear power station in which the same reference letters as those employed in FIGS. 1 and 2 are employed for designating like elements. As the heating system of FIG. 3 is conventional and is moreover in many ways similar to that of FIG. 1, it will be described more briefly than the system FIG. 1.

This heating system comprises, in the main circuit CP, a subcooler SOR and six heaters R₁₁ to R₁₆ fed with steam from drawoffs S₁₁ to S₁₆ respectively. The heater R₁₆ is also fed with the steam separated by a phase separator SP₁₁ from the condensates of a superheater SU (not shown). A main regulating valve SR₁₁ and a safety regulating valve V₁₁ which are controlled as a function of the level in the superheater enable the condensates of the latter to be sent to the phase separator SP₁₁ or to the following condenser as required, as described before. The following heater R₁₅ is fed with the steam separated from the condensates of the heater R₁₆ by a phase separator SP₁₂. A main regulating valve SR₁₂ and a safety regulating valve V₁₂ controlled by a level regulator RN₁₁ are provided.

The condensates of the heater R₁₅ are sent to a reservoir DRT for recovering the drains through a main regulating valve SR₁₃. In the case of an incident, a safety regulating valve V₁₃ enables these condensates to be sent directly to the condenser. The reservoir DRT also receives the condensates of a drier SE (not shown) through a main regulating valve SR₁₅. A safety regulating valve V₁₅ controlled in the same way as the valve SR₁₅ as a function of the level in the drier, enables these condensates to be sent directly to the condenser if necessary. The reservoir DRT receives the condensates of the heater R₁₄. A safety regulating valve V₁₄ controlled by the level regulator R₁₄ is provided for sending the condensates to the condenser if necessary.

The contents of the reservoir DRT are re-injected by way of a condensate withdrawing valve PR in the main circuit CP between the feed pump PA and the heater R₁₄, through a main regulating valve SR₁₆ which is controlled by a level regulator RN₁₃ associated with the reservoir DRT. This regulator RN₁₃ also controls a safety regulating valve V₁₇ whereby the condensates of the reservoir DRT may be sent to the condenser.

The condensates of the heater R₁₃ are sent, either to a phase separator SP₁₃ through a main regulating valve SR₁₇ or to the condenser through a safety regulating valve V₁₇ as a function of the control of the level regulator RN₁₅ of the heater R₁₃. The condensates of the heater R₁₂ are sent, either directly to the subheater SOR and from there to the condenser through a main regulation valve SR₁₈ or directly to the condenser through a safety regulating valve V₁₈ as a function of the control of the level regulator RN₁₆ of the heater R₁₂.

In the heating system according to the invention for a nuclear power station, as shown in FIG. 4, biphase turbines TB₁₁, TB₁₂, TB₁₃, TB₁₄ and TB₁₅ are respectively substituted for the main regulating valves SR₁₁, SR₁₂, SR₁₃ SR₁₇ and SR₁₈ and for the phase separators SP₁₁, SP₁₂ and SP₁₃ which are eliminated.

The steam separated by the turbines TB₁₁ and TB₁₂ is fed respectively to the heaters R₁₆ and R₁₅ whereas the water joins the respective condensates of these heaters so as to be fed to the following turbines TB₁₂ and TB₁₃ respectively. The steam separated by the biphase turbine TB₁₃ is sent to the reservoir DRT, whereas the water is sent upstream of the condensates-withdrawing pump PR so as to be re-injected with the drains of the reservoir DRT in the main circuit CP.

The biphase turbine TB₁₄ separates the steam from the condensates of the heater R₁₃ and sends the steam to the steam side of the heater R₁₃, whereas the water joins the condensates of this heater. This mixture is introduced in the biphase turbine TB₁₅ and the steam separated in the latter is sent to the steam zone of the heater R₁₁. The water joins the condensates of this heater and the mixture thus formed is sent to the sub-cooler SOR.

It will be understood that, as in the case of FIG. 2, the biphase turbines TB₁₁ to TB₁₅ are fed as a function of the level in the condensation exchanger from which they receive the condensates, by adjustment of the position of their respective regulator V'₁₁, V'₁₂, V'₁₃, V'₁₄ and V'₁₅. Likewise, also in this example, the power of the mixture of water and steam in each of the turbines is received on a common shaft A for driving auxiliary means or individually on the shaft of each turbine.

Thus, the heating system employing biphase turbines according to the invention both permits a cascade feeding of the heaters with the steam taken from the condensates of a preceding heater or from a superheater and provides additional mechanical power. Consequently, this improves the overall efficiency of the energy producing plant with which the heating system is associated.

Apart from this advantage in respect of efficiency, which may be expressed as an additional supply of power of 0.5 to 0.8%, the heating system according to the invention enables the static phase separators of the heating system of the prior art to be eliminated, since it is the biphase turbines themselves which effect the separation. As a result of just this fact, the aforementioned erosion phenomena separators are eliminated and the piping is simplified. 

I claim:
 1. A system for utilizing condensates of a steam turbine of an energy producing plant, comprising at least one condensation heat exchanger whose condensates are expanded toward a lower pressure exchanger, wherein said system comprises at least one biphase turbine disposed between said condensation heat exchanger and the lower pressure exchanger and fed with the condensates of said condensation heat exchanger.
 2. A system as claimed in claim 1, comprising a series of condensation heat exchangers disposed in cascade and fed with steam from turbine drawoffs at pressures which progressively decrease from the steam boiler side to the condensor side of the power plant, the system comprising a plurality of biphase turbines disposed in cascade, the first turbine of said plurality being fed by the drain of the last of the series of said condensation heat exchangers at the highest pressure whereas the following turbines are each fed at least in part with the outlet liquid of the biphase turbine which precedes it.
 3. A system as claimed in claim 2, wherein certain of said biphase turbines are fed both with the outlet liquid of other biphase turbines and with the condensates of the condensation heat exchangers which precede them on the upstream side.
 4. A system as claimed in claim 3, comprising an intermediate mixing heater, wherein a biphase turbine associated with a condensation heat exchanger disposed immediately downstream of said mixing heater is fed solely with the outlet liquid of the biphase turbine feeding the said mixing heater.
 5. A system as claimed in claim 2 or 3, comprising a super-heater upstream of the condensation heat exchanger operating at the highest pressure, wherein the system is provided with a biphase turbine between said super-heater and said condensation heat exchanger.
 6. A system as claimed in claim 2, 3, or 4 comprising a biphase turbine associated with each of the plurality of consecutive condensation heat exchangers.
 7. A system as claimed in claim 1, 2, 3, or 4 wherein the biphase turbines are coupled to a common power shaft.
 8. A system as claimed in claim 1, 2, 3, or 4 wherein said biphase turbine includes a regulator regulating the feed thereto, each said regulator being controlled by a further regulator regulating the level of the condensates in said condensation exchanger. 